A cannon-fired missile typically operates in a series of steps. A first launching charge provides the pressure required to eject the missile from a gun barrel in a desired direction. After this discharge step, the missile initiates a propulsion system, such as a propulsion force comes from an engine contained in the missile body. Engines used in missile design include rocket engines, gas turbine engines, and pulse jet engines, among others. Operation of a gas turbine or other air-breathing engine may require that the missile provide those systems typical of turbine operation, including for example, an air flow system from the exterior region of the missile to an engine inlet. Thus, designs for cannon-fired missiles often call for openings in the missile body that allow air to be pulled from the exterior of the missile and into the turbine engine section. In typical turbine engine operation, the air (or a portion of the air) that is pulled into the turbine engine section is then compressed, mixed with fuel, ignited, and discharged through a nozzle section to propel the missile.
A missile structure, and particularly those missile structures associated with cannon-fired missiles, may be subjected to high G forces during launching, including set back and balloting forces. Additionally, post-launching actions, such as air guide deployment and engine start-up, may further stress the missile structure. During flight missiles may also encounter the general turbulence and stresses associated with projectile flight. However, openings in the missile skin, such as an opening to allow air flow from the exterior of the missile to the interior of the missile, may present points of weakness in the missile structure.
Space and weight are often important factors in turbine engine design. This minimal engine weight then allows, among other advantages, for the range of the missile to be extended.